(function rem100(doc, win, setFontSize = 16) {
  var docEl = doc.documentElement,
    resizeEvt = "orientationchange" in window ? "orientationchange" : "resize",
    recalc = function () {
      var clientWidth = docEl.clientWidth;
      if (!clientWidth) {
        return;
      }
      docEl.style.fontSize = (setFontSize * clientWidth) / 1920 + "px";
      console.log("docEl.style.fontSize", docEl.style.fontSize);
    };

  recalc();
  if (!doc.addEventListener) return;
  win.addEventListener(resizeEvt, recalc, false);
  doc.addEventListener("DOMContentLoaded", recalc, false);
})(document, window);
